Process of making seamless hollow bodies of refractory metals



April l0, 1945., R. LowlT 2,373,405

PROCESS OF MAKING SEAMLESS HOLLOW BODIES OF REFRACTORY METALS Filed Feb.14, 1941 warm/6 0.//7 6.44m caff INVENTOR. /U' 0W/7 ATTORNEY Patentedpr. l0, 1945 NETE@ STATES maar ottica PROCESS 0F MAKING SEAMLESS HOLLOWBODIES 0F REFRACTORY METALS Rudolf Lowit, Union City, N. l., assignor toCallite Tungsten Corporation, Union City, N. d., a oorporation ofDelaware l Claims.A

The present invention relates to the manufacture of seamless tubes ofrefractory metals such as tungsten, molybdenum, tantalum and columbium.

It is an object of this invention to provide seamless tubes, tubularparts, or hollow bodies of various cross-sectional shape, which areuseful in operations Where high temperatures are encountered. For thispurpose the high melting point metals above mentioned are distinctlysuitu able but hitherto no practical method has been devised formanufacturing them .in tubular form.

it is contemplated by the present invention to form a hollow body of themetals contained in the group including' tungsten, molybdenum, tantaluni, and their alloys or composite bodies of said metals, by pressinga body from the metallic powder about a forming core. The pressed bodyis then subjected to a sintering process during which the metallicpowder sinters and frits into a coherent body capable oi being forged,rolled or swaged, and subsequently drawn. The forming core may beremoved as an incident to the temperatures employed in sintering or:ritting the metallic body, which 'temperatures are suiilciently high tomelt or volatilize out the material of which the forming core is made.

lr' the forming core be of metal, it should ordinarily have a meltingpoint considerably dlerent from that of the metal of which the tube isto be formed. lt should also have a coeicient of expansion not greaterthan said tube metal and preferably considerably lower. Furthermore, thecore material, if metal, should either be of a metal that will notreadily alloy nor form compounds with the tube metal or else it shouldbe coated or sleeved with such va metal or other compound to preventsuch alloying or reaction. Suitable for such cores are alloys of nickel,iron, chromium, etc., and particularly the alloy of nickel and steelknown as Invar which has a nickel content of 36% and a very lowcoedicient of expansion.

I have found various compounds of silicon, such as quartz, pyrex glass,or other boro-silicate glasses, to be especially suitable for use as aformingv core. Sillimanite and carborundum may also be satisfactorilyused.

According to the preferred method of the invention, a die of the desiredshape is partially lled with a refractory metal in nely divided form.This is then tamped down and a rod, which is to be the forming core, isplaced centrally on this metal, More of the same metal powder is thenplaced in the die in such manner that the forming core is disposedWithin the mass. 55

The whole assemblage is then subjected to considerable pressure so as toform the metal powders into a compact body about the forming core. Thisbody is then removed and subjected to a preliminary sintering at atemperature suflicient to bring the metallic powders into a coherentbody with the forming core still disposed therein in a neutral orreducing atmosphere or in a vacuum. At this point the metallic bodyattains sufficient coherence to be handled, and it is then placedbetween electric termini and electric current is passed directly throughit until it is heated .to a point short of the fusing temperature. Thisheating may be done by passing a current directly through the body, orby any other means such as by high frequency induction. During thistreatment the core crops out, melts out, or distils ofi according to itsnature, through a properly provided opening, and there results acoherent, strong, hollow, metallic body.

The drawing presents a flow diagram showing the various steps of theprocess.

es shown in the diagram, the die or mould is i'lrst filled approximatelyhalf ull of finely divided metal such as molybdenum which is tampeddown. A rod of borosilicate glass is then centered in the die on top ofthe metal powder. More of the metal powder is then added to lill thedie, the glass rod remaining in the center' thereof. The metal powderthus in the die is then subjected to a high pressure, hydraulic orotherwise, ci the order of l@ or 213 tons per square inch, or evenhigher, in order to compress and densely compact the metal powder asuniformly as possible. The compacted mass with the glass core stili inplace is then sinte'red by placing lt in a furnace in a neutral orreducing atmosphere or in a vacuum. rIhe body may be mounted during thesintering step in a vertical position between two electrodes and heatedby direct pas sage of current to slightly below the meltingpclnt of themetal. Below this temperature the glass rod melts and flows out or dropsout, leaving a smooth, clean passage through the metal body.

The molybdenum body with the cylindrical opening so formed by theremoval of the borosilicate glass rod is then removed from the furnace.A rod. which may be of metal or other suitable material, is theninserted in the hole in the center of the body and the assemblage soformed is then introduced into a swaging machine and swaged down inknown manner. When the tubing has been reduced to the desired size, thecore is removed, mechanically-or otherwise, and there results a strongmolybdenum tube of fibrous *VVeonstruenon-i innescare! swinging;thezbodymay 1 1 v t @internmlybzlemm,v thereby1s,inf rr1eSaid 1 f 1 I f1 be relied or: forsean Thermal stier may bei draw-g 1 1drlwnzbvdyandmeltingrwt ,Seid bOQSH-f 11 m511iv1-1--irv -*rvf1 fffcateglasscorepinsertingafmetalrodinto'the i '11' IfiThe proceduresbeveideseribed for molybdenum 1 'hollowleft by'siaidfe: endiswaeng @WMOfie-11 11 1 *Ywithslightlmodincationsasltotemneratureandv/Siredsze@ 1 11 i ienne; win: 'also' apply for mngsten; cantslum,1 ed.1 l 1 1 1 12;method of; making aI seamless :tope @f1 1 1 1 f iiunlloium,1 composite:bodies of i 'said metals; my f v 1molyhdemim,v tungsten nr; likerefractory metal f their rim-emi? metal o 2 Hnweyer, if f tungsten, y 11comprisinspressinggseid refractory meter about imetiis:usedand:aipyrexgiasseorethere wo111d-1ia1borosilicategiassmdsnteringsaid: pressed 1 ne little,1 iff any; changenecessarmvl'yrex'glaiss; i metal in 1 a neutral; or; 1 educingatmospliereI by 1 forinstiance,- will; melt Eand Iflow;atlabout; i200? iI mounting said body between electrodes and pass'.v

wriesiiicen oxide distiisiouti at temperetureso i ing 1'ciurrentthrofueh Iseid:sirnre'red body, thereby s 1 l "theorder of 1BGD" Corhighen r: 1 1 1vheating; i1, toia temperature slightlybelowlthe 1 1 y1 1 y z 1 y 1 l f 1 It; is witlriin the lconteignplation of theirivveifltiong I melting point of: the metal@ at the same timemeltf i"'that the forr'ning core'mayevenbef ois.1 metal 'l5 ing outy theIborosilioate1glass rod; then inserting l f i v iraving a meltingpointashign :aslorzhignerthan: 1 t 1 i a rodofmetaiinthe passageformedby the said f Ithe meltingpoint of ItheI tube metal; It 'snouicLI1 1 1 1 1 f vnd;drawing1 said 1 sus@ I 1 Iimameiong and zshrmid niet@berofametaiithat woud; 1 i 1 r 13. @'Ihemethod: of making@ Seamlesstubing ie! l *alloy with thetube' metal; For instance, if; the 291 densemolybdcnummetalcom rising the :steps o1 i tube metal ismolybderium,itWouldbe quite prac-5' 1' cnmpaeting, molybdenum 1 I 1er.l 1 powder u 1 e1 l Itical and within the souper of@ the' invention to use i 1 pressure;of the ,order of; 101tof21l1tons perso 1 r l f a rod oftungstenproperlyfcoated lorsleeved; with i i 1 inch; about 1a 1 core oforosilieate glass; heating 1 highI melting point oxides susha's, theoxidego` 1 1 said body so ffoi'med to a, temperaturejustbelow i iberyllium; magnesiom1,izirconium,; ori thorium; ias@ i251 the v1reltizns paint iof molybdenum and above Ithe f v 1 the forming' leere;iaitho'u'gh tungstenhas La cm1-2 i i me? l point Ofi the said elassfcordthereby :sine f1siderablyhigherimelting poiritthan has molyb-1 wteringthe powdered molybdenum andmelting :out l l deniim; Its coefficient ofexpansion; lfilowever,v isi the 1saidglasscore1; inserting 1a metal rodinto the 1 f close vto that 'olfI pyrex glass 1and because ofI itsk lopening left by Saidmeltedoutcore;mechanically 1 i vcoatingit; Wilinot:ailoywith molybdenuinp "Ihere 301 WOIkine Said sintered body; about saidmetal rod@ 1 l are Icertain practical advantages in 'usinga tung l 1 iuntil Said bodyis reduced tovdensve metallic conel 1`fsten'rodinitnisimannersiricethe:tube:maybe1I ldition? andthenzremovinggseidmetal rod.1 .11 i y 11 1 1 formed g about lit andalafterlthe sintering step, the l 1 whole assembly centered; about? thetungsten ,coi-el i 1 which stili rerlnainsmay he swaged; :forged: rolled1 i and drawnw'ithout: the necessity 1 ofzremovng the 1 core; andinserting; a newI rodi in place thereof.: 1 After the sw'aging,vrolling,1 forging and drawing l inea die of raisuitabl fllmll fillingSdlde ap* 1 isI completed; however; 1rthe tungsteri1 core kmay lproximately lhalfI fullI withnelyj divided rerse I be removedmechanically; 1I may :also vuse ias a i 4i@ tory metalicenterng: a rodof borosiiiceteI glass;

core material, Where the body material is molybupon said metal in saiddie, completely filling denum, a rod of molybdenum coated with high saiddie with more of the nely divided refractory melting point oxides. metalwith the glass rod remaining centered Having thus described myinvention, what I 45 therein, subjecting the powdered metal in saidclaim is: l 1 die to a pressure of approximately 10 to 20 tons 1. Themethod of forming a seamless molybper square inch, and then heating toa, temdenum tube which comprises pressing nely perature slightly belowthe melting point of the divided molybdenum powder in a die about avmetal, thereby sintering said metal and melting borosilicate glass core,heating said pressed body 50 out said rod of borosilicate glass. soformed to a temperature just below the melt- RUDOLF LOWIT.

o 14; 11i/retired of making; a Is1eam111ess1 mbe sf tu group; consisting1 off 1 tungsten, f molybdennm "1 tantaium; columbium and the alloys;and com: posite bodiesI ofi said metals capable :or beine ilmechenieallrworkd that consists ,in first Pmi/id

